On-board auxiliary hydraulic systems for work vehicles are well known in the art with agricultural equipment such as tractors and construction equipment such as excavators typically providing fully integrated arrangements. These integrated auxiliary hydraulic systems can be supplied either by the work vehicle's main hydraulic source, if it has sufficient capacity beyond hydrostatic drive and other primary demands or by a separate dedicated pump. In either case the auxiliary hydraulic system includes a number of proportional and directional valves for controlling the hydraulic fluid flow to the auxiliary equipment. U.S. Pat. No. 4,043,099 to Cheatum describes such an auxiliary hydraulic system that utilizes a tractor's main hydraulic source to power a pair of auxiliary actuators that automate the movement of the windrow pick-up mechanism and swingable tongue of a pull type agricultural harvesting machine.
It is less common for road going vehicles to include an auxiliary hydraulic system since the integrated hydraulic pumps required for hydrostatic drive and other primary demands are not available. The lack of a primary demand system dictates the usage of a dedicated auxiliary pump which can be either engine driven or incorporated in a self-contained, electric motor driven module. Conventional engine driven systems require a pump mounting and drive system, a decoupling arrangement such as a clutch, distribution lines, switching control and proportional valves. Electric motor driven configurations do not require a decoupling arrangement but add electric motors, extra batteries and associated wiring to the additional complexity. Unless a piece of auxiliary equipment which requires hydraulic supply, such as a snow plow or dump box, has been installed, the associated cost of an auxiliary hydraulic system has been generally deemed to be prohibitive. Therefore, road going, general purpose, light and medium duty pick-up trucks of weight classifications one or two do not generally include auxiliary hydraulic systems even as a customer purchased option.
Some exceptions do exist, including the Mercedes-Benz Unimog™ which is a heavy duty utility truck of weight class two or three, capable of both on and off road usage. In addition to general purpose use the Unimog™ is also a very popular military vehicle and is utilized as a base for fire vehicles and the like. The Unimog™ is unique in that it crosses the boundary between pure utility vehicles such as agricultural tractors, and road going vehicles such as pick-up trucks. Like an agricultural tractor, it offers fully locked all wheel drive, mechanical power take-off and most significantly, auxiliary hydraulic supply provided by an engine driven dedicated pump.
Aftermarket auxiliary equipment for light and medium duty pick-up trucks of weight classifications one or two, such as snow plows, lift gates and dump boxes commonly include self-contained, electric motor driven hydraulic supplies. In the case of a snow plow the hydraulic supply represents half of the total system cost. U.S. Pat. No. 3,706,144 to Miceli describes a simple snow plow system for use on a light truck that is targeted at providing a less expensive solution to commercial removal equipment. However, although simplistic, the Miceli prior art still requires an electric motor-driven pump, selector valve, angle control valve, plow-lowering valve, reservoir tank and associated valve solenoids in addition to the plow, mounting structure and hydraulic cylinders. If a number of pieces of auxiliary equipment are added to a pick-up truck then it is forced to carry an equal number of associated electric motor driven hydraulic supplies. Stand alone, self-contained, electric motor driven auxiliary hydraulic modules are also available for mounting on vehicles to supply any number of remote auxiliary equipment requirements such as log splitters, hydraulic lift cylinders and the like. Both the dedicated pump and stand alone electric motor driven hydraulic supply systems commonly utilize a pair of solenoid operated poppet valves to provide flow control. These poppet valves provide on-off control and direction switching but have no proportional flow capability as applications such as snow plows can operate adequately without velocity control.
The facility for rotary mechanical power take off is another common option offered on heavier duty trucks of weight class three and above, when either mechanical drive is required for auxiliary equipment such as winches, mechanical lifts, generator sets, feed mixers and the like or engine driven auxiliary hydraulic pumps as previously described. These power take off units provide appropriate gear reductions to achieve predetermined rotary speeds, such as the agricultural standard requirement of 540 revolutions per minute, and a clutching methodology to decouple the drive. For example, U.S. Pat. No. 6,073,502 to Wallace describes a compact, high horsepower power take off that includes an air actuated shifting mechanism for connecting and disconnecting the system from the engine. Wallace additionally describes how the power take off can be used to drive a hydraulic pump so that the more demanding hydraulic applications of these heavier duty trucks, such as dump beds, aerial buckets, tilt back car carriers and wrecker booms, can be supplied. Again, because of the prohibitive costs associated with mechanical power take off, road going, general purpose, light and medium duty pick-up trucks of weight classifications one or two do not generally include this type of capability although a number of aftermarket manufacturers do offer some limited compatibility units. A major disadvantage of these power take off units is that their output shaft speed varies proportionally with the vehicle's engine speed.
Most off-vehicle light and medium duty utility equipment comes with its own power supply, independent of the final drive configuration. For instance, wood splitters, hydraulic lifts and dump box trailers utilize hydraulic final drive but are powered by dedicated internal combustion engines or electric motors. Other equipment, such as wood chippers, water pumps, electrical generators, power washers and post-hole diggers, tends to be directly mechanically driven using either dedicated internal combustion engines or electric motors. In either case, a large collection of utility equipment tends to result in a large number of associated prime movers with all of the associated maintenance demands such as oil and air filter changes. In the majority of non-industrial applications, as around the home, these prime movers tend to be subjected to relatively low usage, resulting in an extremely poor value proposition.
Pick-up trucks have become extremely popular for light utility use and even regular transportation. This has significantly increased access to these heavier duty vehicles up to weight class two, which offer high power, occasionally diesel, internal combustion engines that are highly capable beyond their primary motivation application. If the internal combustion engine of a pick-up truck could be arranged with simple access for powering on-board and off-board auxiliary equipment such as snow plows, dump boxes and wood splitters, then significant increased utility and cost savings would be realized.